Conveyor belts formed as loops for transporting materials along a forward stretch of the loop often require cleaning along the return stretch of the loop. For that purpose, various devices such as scrapers and brushes have been used, with varied degrees of success.
Industrial belt conveyors, which are used to convey coal, gravel and other particulate material, require cleaning of the return stretch of the loop, to rid the belt of embedded or stuck-on particles. A particularly effective cleaner for belts of that kind relies on a ribbed cleaning roller, usually of polymeric material such as polyurethane. The ribs of the roller just "kiss" the belt and sweep over the belt at high speed to strip the particles from the belt. Characteristically, such belts are quite thick and very stiff. If any significant amount of pressure of the cleaning roller were to develop against the conveyor belt, various troubles may arise. The cleaning roller smokes, and the drives of the roller and the belt conveyor are overloaded and damaged, or the drive is shut down by protective gear.